The present invention relates to nuclear reactors and the containment therefor, the invention more particularly being directed to passive heat removal from the containment in the event of one or more types of system malfunctions.
Commonly assigned application Ser. No. 07/325,729 filed Mar. 20, 1989 discloses a nuclear reactor system which on occurrence of an accident, e.g., loss of coolant in the reactor vessel, break in main steam pipe etc operates to dissipate initial heat generated incident the occurrence and also to dissipate the decay heat, i.e., the heat produced by fuel rod decay reactions which persist for a period of time of days or even weeks duration.
In the prior disclosed system, initial heat can be dissipated by venting steam generated in the pressure vessel to a suppression pool in a closed space wherein the steam condenses and heat is transferred to water in the pool. After the pressure in the reactor vessel reduces to a certain magnitude, water in an elevated pool will flow by force of gravity into the reactor vessel to replace any loss of coolant therein as may have taken place, the elevation height of the pool being such as to provide a flow head sufficient to overcome the reduced pressure value in the reactor vessel. In the prior system, one or more isolation condensers are submerged in a large supply of water disposed elevated with respect to the pressure vessel, the water in turn being open to atmosphere so that any boiling thereof caused by a heat transfer from a heated medium passing through the condenser can be passed to atmosphere. This heat transfer results from venting the pressure vessel to the isolation condenser through an isolation line connecting the pressure vessel with the inlet side of the condenser, the condenser in this case serving to dissipate initial heat. Condensate from the isolation condenser is returned to the pressure vessel by a return line connecting the condenser outlet with the pressure vessel.
A depressurization line in the system also can be opened to vent steam to the drywell surrounding the pressure vessel and in time the steam pressure in the drywell will, due to vessel cooling, be higher than that in the vessel. As a result, steam from the drywell will pass through the depressurization line, through the pressure vessel, the isolation line and into the isolation condenser where it will be condensed. In this manner and over a period of time, decay heat is dissipated.
The arrangement and operation of the prior disclosed system involves the need during an accident to open valves, either automatically or manually, in one or both of the isolation line and condensate return line, and in a condenser vent line as a condition for cooling to be carried out in the isolation condenser. Since automated controls and/or human intervention are subject to failure, isolation condenser operation is only passive to the extent that these components operate. Also, it is noted that it is only sometime after accident occurrence that heat dissipation from the containment space through the isolation condensers is initiated.